MySQL learning Day1 DDL, DML, DQL basic query

Day1

One 、DDL、DML

1.1 MySQL Log in to exit

What is? sql？
Structured Query Language： Structured query language
In fact, it defines the rules for operating all relational databases

1.2 General grammar

1.3 SQL classification

1.4 DDL Operating the database _ establish & Inquire about

DDL(Data Definition Language) Data definition language ：

 Used to define database objects ： database , surface , Column, etc. , keyword create、drop、alter etc. 

1. Operating the database ：CRUD

   *C(create) : establish 
   * R(Retrieve)： Inquire about   show databases  Query all databases 
   * U(Update): modify 
   * D(Delete) Delete 
   *  Using a database 
   

1.4 DDL Operating the database _ modify 、 Delete 、 Use

1.5 DDL Operation table - Inquire about 、 establish

show tables： Query all table names in a database
desc Table name ： Query table structure
Copy table :create table indicate like Copied indication

1.6 DDL Operation table - modify 、 Delete

1.6 DML_ add to 、 Delete —— Modifying data

Modifying data

Two 、DQL

2.1 Inquire about

2.2 Conditions of the query

CREATE TABLE student (

id INT, --  Number 
NAME VARCHAR(20), --  full name 
age INT, --  Age 
sex VARCHAR(5), --  Gender 

address VARCHAR(100), --  Address 

math INT, --  mathematics 

english INT --  English 
);
INSERT INTO student (id, NAME, age, sex, address, math, english) VALUES (1, ' Jack ma, ',55,' male ',' Hangzhou ' ,66,78), 
(2,' ma ',45, ' Woman ',' Shenzhen ',98,87),(3, ' Ma Jingtao ',55,' male ',' Hong Kong ',56,77), (4, ' Liu Yan ',20, ' Woman ', ' hunan ',76,65), 
(5,' Liu Qing ',20, ' male ',' hunan ' ,86,NULL),(6, ' Lau Andy ',57,' male ',' Hong Kong ',99,99), (7, ' Mard ' ,22, ' Woman ',' Hong Kong ',99,99), 
(8, ' De Marcia ',18, ' male ', ' nanjing ',56,65);


SELECT * FROM student;
--  Search for name and age 
SELECT NAME,age FROM student;
--  Remove duplicate result sets 
SELECT DISTINCT address FROM student;

SELECT NAME,address FROM student;

--  Calculation math and english Sum of scores 
SELECT NAME,math,english,math + english FROM student;
--  If there is a null Operations involved , The results are all null IFNULL function 
SELECT NAME,math,english,math + IFNULL (english,0) FROM student;

--  names 
SELECT NAME,math  mathematics ,english  English ,math + IFNULL (english,0)  Total score  FROM student;


--  Query age is greater than 20
SELECT * FROM student WHERE age > 20;
SELECT * FROM student WHERE age >= 20;
--  Inquiry age is not equal to 20
SELECT * FROM student WHERE age != 20;
SELECT * FROM student WHERE age <> 20;

--  Age   Greater than or equal to 20  Less than or equal to 30
SELECT * FROM student WHERE age >=20 && age <=30;
SELECT * FROM student WHERE age BETWEEN 20 AND 30;

--  Check age 22 year ,18 year ,25 Age information 
SELECT * FROM student WHERE age = 22 OR age = 18 OR age = 25;
SELECT * FROM student WHERE age IN (22,18,25);

--  The English score is null ,null Value cannot be used = !=  Judge 
SELECT * FROM student WHERE english IS NULL;
--  The English score is not null
SELECT * FROM student WHERE english IS NOT NULL;

--  Find out what's the name of Ma ？
SELECT * FROM student WHERE NAME LIKE ' Horse %';
--  The second word in the query name is the person 
SELECT *FROM student WHERE NAME LIKE '_ turn %';
--  Query the person whose name contains the horse 
SELECT * FROM student WHERE NAME LIKE '% Horse %';